Drive regulation and delay control in display systems

ABSTRACT

Apparatus addressing multi-position display devices directly from semiconductor integrated circuits and driving the display electrodes without exceeding the limitation on voltage excursions for the outputs of such circuits. The apparatus develops and applies to threshold-responsive display devices, including gas discharge display tubes or display panels, only the amount of voltage that is needed to operate them. Potential for operating the device is accumulated in steps until the device fires, it being applied to the display electrodes of the device in response to open-circuit input signals. The potential is regulated to maintain ionization delay in the device as a certain fraction of the display period and the required selection voltages for the electrodes of the device are minimized. The potential for driving the cathodes is developed across a capacitance common to all of them, and a regulator circuit coupled to it and to the cathode drivers automatically increases the bias until the device fires. The potential that proves to be necessary to operate a device is stored for continued operation of it. The driver for a cathode element that is frequently operated alone is coupled to the regulator circuit by a high impedance connection for increasing the energizing potential sufficiently to ensure ionization. The anodes are driven from semiconductor logic circuit often without intermediate circuit elements.

United States Patent 191 Ogle DRIVE REGULATION AND DELAY CONTROL INDISPLAY SYSTEMS [75] Inventor: James Ogle, Neshanic Station,

[73] Assignee: Burrbughs Corporation, Detroit,

Mich.

[22] Filed: July 13, 1972 [21] Appl. N0.: 271,576

[52] U.S. Cl. 315/169 TV, 315/169 R [51] Int. Cl. H05b 37/00 [58] Fieldof Search 315/169 R, 169 TV [56] References Cited UNITED STATES PATENTS3,573,542 4/1971 Mayer et al..... 315/169 R 3,626,244 12/1971 Holz315/169 R 3,665,246 5/1972 Kurahashi et al. 315/169 R PrimaryExaminer-Herman Karl Saalbach Assistant ExaminerLawrence J. DahlAttorney, Agent, or Firm-Robert A. Green; Edward.

G. Fiorito; Paul W. Fish 57 ABSTRACT Apparatus addressing multi-positiondisplay devices May 14, 1974 directly from semiconductor integratedcircuits and driving the display electrodes without exceeding thelimitation on voltage excursions for the outputs of such circuits. Theapparatus develops and applies to threshold-responsive display devices,including gas discharge d-isplay tubes or display panels, only theamount of voltage that is needed to operate them. Po-

tential for operating the device is accumulated in steps until thedevice fires, it being applied to the display electrodes of the devicein response to open-circuit input signals. The potential is regulated tomaintain ionization delay in the device as a certain fraction of thedisplay period and the required selection voltages for the electrodes ofthe device are minimized.

The potential for driving the cathodes is developed across a capacitancecommon to all of them, and a regulator circuit coupled to it and to thecathode drivers automatically increases the bias until the device tires.The potential that proves to be necessary to operate a device is storedfor'continued operation of it. The driver for a cathode element that isfrequently operated alone is coupled to the regulator circuit by a highimpedance connection for increasing the energizing potentialsufficiently to ensure ionization. The anodes are driven fromsemiconductor logic circuit often without intermediate circuit elements.

6 Claims, 5 Drawing Figures DRIVE REGULATION AND DELAY CONTROL INDISPLAY SYSTEMS BACKGROUND OF THE INVENTION This invention relates toapparatus for operating segmented-electrode display devices which arethreshold- I responsive to selection signals applied to them, includinggas discharge display tubes and display panels.

like and to driving display elements thereof without exceeding thevoltage limitations on the circuits employed.

Various segmented-electrode display devices have been-developed inrecent years for use as readout indicators for electronic calculatorsand the like. One such device is the PANAPLEX panel display which is amultiple-position gas discharge device having a plurality of segmenteddisplay cathodes and a plurality of associated anode electrodes. Suchdisplay panels usually include several groups of cathode segments, withlike segments of the different groups being interconnected, and an anodeelectrode associated with each group'of cathodes.

In a recently developed version of the PANAPLEX panel display, thecathode elements are deposited or formed along the front surface of aninsulating base plate and planaranode electrodes are spaced closelyabove the cathodes. A relatively large difference in potential betweenan anode and one or more cathodes is required initially to ionize adisplay position, while a lower potential across them will sustain thedischarge. It has been discovered,-however, that either theanodes or thecathodes thereof, if both are suitably biased, can be operated bysignals which do not'exce'ed the maximum voltage excursions that areallowed on the outputs of some metal-oxide semiconductor (MOS)integrated circuits.

Such MOS integrated form of calculator circuits, decoder circuits,counters, registers, and the like. Substantial economies would beobtained if the display positions of such devices could be eitheraddressed or selected directly from MOS circuits with a minimum amountof intermediate amplifying or coupling circuitry being required.

A condition precedent to the use of suchlow voltage signals is that theelectrodes of the device-be biased toward discharge as much as possiblewithout causing spurious discharges. Higher voltages also have to bemade available on one set of the electrodes for initial ionization andre-ionization without violating the allowable voltage ratings on the MOSor other low voltage signal source.

The total potential required for initially ionizing and for re-ionizingthe display positions in gas discharge display panels, however, varieswith the gas pressure and with operating temperature. It also can varysignifi, cantly from tube to tube. A set of bias voltages provided toallow the electrodes of one lot of such devices to be addressed ordriven with minimum possible signal voltages may not be sufficient ormay exceed the potential required to operate another lot of tubes of thesame. general type.

circuits are available in the SUMMARY OF THE INVENTION Accordingly, anobject of the invention is to simplify and reduce the cost of addressingand driving multipleposition display devices or panels.

Another object is to address the display positions of gas dischargedevices from semiconductor integrated circuits or the like withoutexceeding voltage limitations on the circuits.

A further objectof the invention is to regulate the drive voltageapplied to multiple-position display devices and to control the delay inactivating the display positions in them.

The invention provides apparatus for driving the display electrodes ofmultiple-position display devices and for addressing them directly fromlow voltage signal sources without exceeding the voltage limitations onthe signal source. The'potential for driving the cathodes is developedacross a capacitance common to all of'them and a regulator circuitcoupled to the cathode 7 drivers controls the voltageso that the devicewill fire at the predetermined ionization delay.

A major portion of the voltage applied to the display cathodes in thissystem is stored between display periods for application to the selectedcathodes in succeedingperiod s. This stored reference potential, andconsequently the operating voltage, are adjusted automatically tocompensate for differences in the potential thresholds for differentunits and for threshold changes caused by changes in temperature or modeof operatron.

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTSThedisplay panels described herein are thin, flat, sheet-like memberswhich may have substantiallyany desired shape and size, and may includesubstantially any number of character display positions. The panels mayinclude any suitable ionizable gas such as neon, ar-

' gon, xenon, etc., singly or in combination, with a vapor of a metalsuch as mercury usually included in the gas to minimize cathodesputtering. A wide range of gas pressures may be used, for example, fromabout 20 to about 250 Torr at ambient temperature with about to Torrbeing a commonly used pressure range.

Referring to FIGS. 1-3, a display device 10 embodying the inventionincludes an insulating base plate 20 of glass, ceramic, or the like,with an inexpensive glass being suitable and preferred. A plurality ofconductive connectors or runs 30A to 306 are formed on the top surfaceof the insulating plate 20. The runs 30 are parallel to each other andare aligned with the horizontal axis of the base plate. Seven such runs30A to 30G are shown; however, more or fewer may be provided, the

A second thin layer 40 of insulating material such as glass or ceramicis formed on the conductive runs 30, preferably by a silk-screenprocess, and the second layer 40 includes a plurality of groups of viasor apertures 50A to 50G, each aperture exposing one of the runs 30A to30G. Thus, each group of apertures includes aperture 50A which exposesrun 30A, aperture 508 which exposes run 308, aperture 50C which exposesrun 30C, etc. Four such groups of apertures are illustrated.

Panel-l includes a group of cathode electrodes 60 (A to G) for eachgroup of apertures 50. The cathodes are generally elongated bars orsegments, and they are usually arrayed in a figure 8 pattern, as is wellknown in the art. The cathodes 60 maybe formed on insulating layer 40 bymeans of a silk-screen process using a conductive paste such aspalladium-gold, platinumgold, palladium-silver, or the like. Eachcathodeelement is in contact with one of the runs 30 exposed by one ofthe apertures or vias 50, and it substantially fills the aperture 50 andcovers a portion of layer 40 to achieve the desired shape and size. I Y

The cathodes 60A, 608, etc. may also be formed of discrete strips ofmetal, preferably brazed to a conductive run 30 by means ofa mass ofbrazing material deposited in each of the apertures 50 in the insulatinglayer 40. The brazing material itself may be deposited by a silk-screenprocess. One suitable brazing material is a gold-germanium substanceknown as FORMON and sold by E. l. DuPont de Nemours & Co. The cathodesmay also be formed in any other suitable manner such as by theelectrolytic or electroless plating of nickel or the like or by areplasma spraying through a suitable mask.

Thus, cathodes 60 are preferably thin, flat members which do not projectto any significant extent'above the top surface of insulating layer 40.

Panel 10 includes anode electrodes 90 for the groups of cathodeelectrodes 60. The anode electrodes comprise thin, transparentconductive films of gold, NESA, or the like formed on the lower surface95 of the panel face plate or viewing plate 100 which is made of glass.The anode films are of the order of a few Angstroms thick and, ineffect, are coplanar with the bottom surface 95 of the face plate. Thus,the anodes, for all practical purposes, do not project into the gasdischarge space in the panel. The anode films are generally rectangularin shape, or are otherwise shaped, depending on the orientation of thecathodes. Anodes 90 are dimensioned and positioned so that they overlaythe total area defined by the associated group of cathode electrodes. Ifdesired, each anode 90 may be somewhat narrower and shorter than thearea defined by its cathodes as shown, but in any case, the anode mustoverlay and r be in operative relation with a sufficient portion of eachof its cathodes. Other suitable anode shapes may be 'employed, dependingupon the character and symbol configuration of the cathodes to beoperated.

Preferably, the spacing between each anode and its group of cathodes 60should be of the order of 20 to 25 mils, and the spacing between eachanode and the adjacent group of cathodes should be of the order of 30 to40 mils. With this relationship at the usual pressure range, each anodeis in a favorable operating position with respect to its own cathodes,but is sufficiently re-' mote from adjacent groups of cathodes so thatthe panel may be operatedover a suitably wide range of potentialswithout developing cross-talk between adjacent 'groups .of electrodes.Another factor tending to prevent cross-talk is the location of theanodes in substantially coplanar relation with the surface of the glasscover plate and not projecting into the gas space in which cathode glowtakes place.

Another advantage of the close spacing of each anode to its group ofcathodes, thus providing a thin volume of gas, is that metastable-stateatoms produced in the gas during discharge diffuse to, and are readilyneutralized at, these closely spaced surfaces. In addition, excited orcharged particles are readily swept out through the anode-cathodecircuit path. The tendency for cross-talk to develop is minimized bythese two factors.

The top glass cover plate is of substantially the same length as theinsulating layer 40 and the bottom plate 20, and it is spaced from thebase plate 20 by a rectangular glass frame which isdisposed between thetop glass plate 100 and the insulating layer 40. Frame 110 may be anintegral part of the top and/or bottom plates. The rectangular frameserves thus to provide the desired spacing between eachanode and itsassociated group of cathode electrodes. The top glass plate 100 is alsopreferably slightly wider than the insulating layer 40 and base plate 20so that one edge, say the upper edge, extends beyond the remainder ofthe panel and is accessible to permit the connection of leads to each ofthe anode films 90. The three glass members 20, 100, and 110 are sealedtogether in any suitable-manner, for example, by means of a seal 120formed of a glass frit or the like.

Connection to the runs 30 may be made, as an example, by means ofL-shaped pins or contacts 144 which are embedded in the seal 120 at oneor both ends of the panel.

The panel 10 can be filled with the desired gas atmosphere through atubulation secured to the base plate 20 and communicating with theinterior of the panel through a hole 154 in plate 20 and layer 40, and,generally, mercury is introduced from a glass capsule (not shown) heldin the tubulation and suitably processed at the desired stage in theassembly process.

The invention relates to panel-type segment display devices whichinclude a plurality of groups of cathode electrodes which compriseelongated bars'or segments arrayed in a pattern so that the cathodes ofeach group can be selectively energized to display a character. Forreasons of economy, corresponding electrodes in each group, usuallycathodes, have a common conductor. The anodes are separately energizableand the panel is operated in a multiplex mode of operation. In this modeof operation, operating potential is applied to selected cathodeconductors at time t, and thus to selected'cathode segments, and thefirst anode is energized and a first character is displayed by theenergized cathode segments in the first group. At time t,,, operatingpotential is applied to the same or other cathode conductors and to thesecond anode and a second character isdisplayed by the second group ofcathodes. This same operation is carried out for each characterposition, and it is repeated continually along the entire display panelat a suitable frequency so that stationary but changeable characters canbe displayed.

The display system of FIG. 2 incorporates improved operating apparatusfor a multiple-position display device having several groups of cathodesegments or elements 60 (A-D) interconnected by cathode conductors 30(A-D) and a plurality of associated anode electrodes 90. A digitselecting or addressing switch 200 is connected between a voltage supplyterminal 190 labeled V and each of the anode electrodes 90. The

anode switches are all identical and only one of them is illustrated indetail. The cathode circuit includes current drivers 250 A-D) connectedto the corresponding cathode electrodes 60 (A-D) by leads 290 and tocapacitor 175 ofa biasing circuit by bus 170. Capacitor 175 is connectedat its other end to voltage supply terminal 190 and is in electricalseries with emitter resistor 167 of transistor 165, the collector ofwhich is connected to a negative voltage supply terminal 150 labeled VTransistor 165 serves as the'pass element of a bias regulator circuitincluding feedback bus 160 and is coupled to capacitor 175 whichmaintains bias potential on bus 170 for the cathode drivers.

The voltage switches 200 for addressing anodes 90 and thereby selectinga digit or display position in panel 10 are each controlled by ametal-oxide semiconductor (MOS) transistor 210 having a gate terminal205. These MOS transistors 210 may all be formed on the same MOSintegrated circuit chip, and may be part of a complex multiple-functionintegrated circuit. Similarly, anode switch transistors 210 may befield-effect transistor (FET) units or other suitable low voltage units.The source electrodes of transistors 210 are connected to V terminal190. The drain electrodes 215 are connected directly to the anodeelectrodes. A biasing resistor 220, which holds the anode'belowoperating potential normally, and a reverse-biased clamping diode areconnected between it and a bias terminal 240. The anodes can thusreceive the full voltage swing from V to the most negative voltage thatcan be applied to terminal 240 without violating the rated voltagelimitations on the MOS or FET transistors 210.

The cathode circuit consists of segment current drivers 250 (A-D) and abias voltage regulator including transistor 165 connected in series withcapacitor 175, which stores the bias voltage for the drivers. Cathodedrivers 250 and transistor 165 operate together as a feedback loop todevelop bias voltage across capacitor 175 by conducting current out ofit throughthe collector-emitter circuit of transistor '1 65 until theassociated display device becomes activated.

The current drivers 250 for the cathodes are controlled by MOStransistors 260 or the like, which also may form part of a complexintegrated circuit such as a calculator chip or the like. Furthermore,cathode input transistors 260 may be formed on the same integratedcircuit chip as anode switch transistors 210 even though the anodes andcathodes, themselves, are operated at different voltage levels thatexceed the rated voltage limitations of customary integrated circuits.Capacitors 265 couple the cathode input switches 260 6 to cathodecurrent drivers 285, while isolating both the anode switches 210 and thecathode input switches 260 from the voltage levels on the cathodedrivers. The anode switches 210 and the cathode input switches 260 arethus operated from the same bias point (anode voltage level V,,) and maybe formed on the same integrated circuit chip.

The source electrodes of input transistors 260 for the cathode drivers'are connected to V terminal 190. Their drain electrodes are coupled atjunction 262 to the emitter electrodes of cathode driver transistors 285by capacitors 265 and are coupled to a negative voltage terminal 280labeled V by resistors 275. The emitter electrodes of driver transistors285 are also connected to voltage bus 170' by diodes 270. The collectorelectrodes are connected by leads 290 to connectors 30 (A-D) of cathodeelectrodes 60 (A-D) of the display device and to pull-up bias resistors295, which hold the cathodes above their operating potential normally.The other ends of cathode bias resistors 295 are connected to a bus 180which is coupled to V terminal 190 by a reverse-biased Zener diode 185through leads 187 and 189. The base electrodes of cathode drivertransistors 285 are connected to bus. which connects to the baseelectrode of transistor of the bias voltage regulator.

This system allows direct addressing or selection of the anodes of adisplay device from transistors 210 of an MOS circuit chip or the like,and keeps the voltage swing on the digit output terminals 215 of theintegrated circuit chip strictly within customarily specified voltagelimits for them. Frequently specified voltage limitations on suchcircuits range from a conservative 20 or 25 volts to approximately 30volts or more. The system also is operated by open circuit (negativegoing) selection signals for the cathode segments, which in the case ofMOS data sources are open drain inputs.

Cathode drivers 250 (AD) are selectively enabled when thenormally-conducting transistors 260 of the MOS data source are opened(turned off). This unclamps the input side of coupling capacitor 265which is pulled negative by resistor 275 as shown in waveform 300 ofFIG. 3, it having been held normally at V by that transistor. Thissignal current into resistor 275 appears as emitter current in drivertransistor 285 via coupling capacitor 265and is considerably larger thanthe collector pull-up current through cathode bias resistors 295. Thecollectors, therefore, go increasingly negative during ionization delayuntil transistors 285 become saturated, as indicated by waveform 350 ofFIG. 3. Most of the emitter current of transistors 285 is then drawnfrom their base electrodes and through bus l60-and the regulator 165.The sum of the base currents of all the selected cathode segment drivers250 (A-D) is conducted by resistor 155 and the base of transistor 165which causes a proportionately larger current in emitter resistor 167and charges capacitor more negative.

The ratio between emitter resistor 167 and feedback resistor 155 ofregulator transistor 165 determines the approximate proportion betweenthe re-ionization delay and the digit display period at which the systemwill stabilize. Under typical display conditions with a 200 microseconddigit displayperiod, a segment reionization delay of about 20 to 40microseconds, for example, is usually suitable. After the device fires,transistor 285 comes out of saturation and the major part of its emittercurrent is then drawn from the associated cathode via conductor 30 (A-D)and the collector of the transistor to coupling capacitor 265. Resistors275 will limit the current thus conducted from the display andcapacitors 265 are discharged thereby. Thevoltage on bias storagecapacitor 175 will change little once breakdownoccurs in the devicesince the feedback curtire display period. The recharging current incoupling capacitor 265 will be less and capacitor 175 thus will not bedischarged as much as it was charged, but will This feedback-controlledvoltage is stable once display device 10 becomes activated, since thecharging of capacitor 175 is governed primarily by the reionizationdelay, which decreases as 'the voltage goes more negative and willincrease should it be too positive. The proportion between feedbackresistor 155 and emitter resistor 167 of regulator transistor 165determines this operating point and establishes the bias voltage that isstored across capacitor 175. The operating bias is thus regulated tomaintain the ionization delay as a predetermined fraction of the digitperiod. This allows operation with smaller signals than would berequired for faster ionization, yet ensures that ionization will occurat all selected cathodes.

The apparatus responds effectively 'to the operation of the devicebecause capacitor 175 is charged to increase the driving potential forthe selected cathodes until the device fires and is discharged betweendisplay periods by an amount proportional only to the number of segmentsthat were selected.

The potential acrosscapacitor 175 is applied to cathode drivers 250 bybus 170 as bias potential. This is the potential to which couplingcapacitors 265 of the cathode drivers are recharged between displayperiods and,

hence, the initial bias potential for the drivers during each displayperiod. This potential is changed by regulator transistor 165, asthethreshold potential of the device also changes. This compensates forthe threshold potential of different devices being different or changingwith temperature or mode of operation.

The drawing of FIG. 3 reflects the operation of the display system ofFIG. 2. Waveform 300 represents the voltage excursions at input junction262 of a cathode driver 250. Two cycles 301 and 302 are illustrated,both of which begin at V and are pulled rapidly negative by resistor 175until transistor 285 conducts, charges distributed capacitances, in thecircuit, and then becomes saturated at time t2. Input waveforms 301 and302 are pulled farther negative at a slower rate as current in thebase-emitter circuit of transistor 285 begins to discharge couplingcapacitor 265 during the remaining ionization delay until the devicefires.

Waveform 301 represents operation at equilibrium, in which theionization delay equals the predetermined portion of the display period.Waveform 302 represents instead accumulate negative biasing charge untilthe device fires. I

operation of the device in which the ionization delay exceeds thepredetermined fraction of the display period. At time t3 breakdownoccurs at the selected display position, at which point cathode driver285 comes out of saturation and the base currents of the selecteddrivers which are summed in feedback resistor decrease greatly. Thiscauses a corresponding voltage shift in the emitter circuits of thedrivers and at input junction 262 of the drivers. The input waveformsthen continue to decrease as coupling capacitors 265 are dischargeduntil the end of the display period at time t.,. The input waveformsthen return to V Voltage waveforms 310 and 320 appear on feedbackbusconnected to the base electrodes of cathode driver transistors 285and to the base electrode of regulator transistor 165. They reflect thefeedback current in the base of pass element and in base resistor 155during ionization delay between times t2 and t3 and during operation ofthe device until t4. The amplitude of the feedback current during cycle311 or cycle 312 will depend on how many different cathode segments arebeing driven by cathode drivers 250 (AD) during the particular cycle.Waveform 310 represents operation of a few cathodes and waveform 320represents operation of most of the cathodes. Bias capacitor 175 will becharged more negatively byhigher feedback currents, but will bedischarged proportionately at the end of the cycle when thecorresponding number of coupling capacitors 265 are recharged into it.

Waveforms 330 and 340 represent the voltage excursions on bias voltagebus connected to capacitor and to the coupling capacitors 265 by diodes270. Wavefrom 330 represents the excursion if only one or two differentcathodes are being driven. Waveform 340 represents the larger voltageexcursion when several or all of the different cathode segments orelements are being driven.

Voltage waveform 350 represents the voltage pattern that are applied tothe cathode electrodes on leads 290. When driver 285 begins to conductits collector and the associated cathodes go negative. At time t2 driver285 saturates and its collector therefore follows the voltage on itsbase until the driver fires at time t3. The cathode voltage betweentimes t3 and t4 is relatively constant as the voltage drop across afired display position until the end of the display period. These outputwaveforms 351 and 352 that are applied to cathode leads 290 beginaandend at a voltage determined by pull-upresistors 295 and zener diodeconnected between them and V terminal 190.

Since the ionization delay in segmented gas discharge devices depends inpart on how many cathode segments are energized, a specialized cathodedriver for single segment displays may be desirable. The middle bar orsegment in a figure eight pattern is often operated alone as a minussign, for example. In the cathode circuit of FIG. 4 cathode drivers 250Athrough 250D, etc., are the same as those of the system of FIG. 2, butcathode driver 250G is connected differently to the regulator circuitand may have a higher value cathode pull-up resistor 297 for easierdriving, if desired.

In the cathode driver 2506 of FIG. 4 for cathodes 60G, a resistor 287and a capacitor 289 are coupled in parallel between the base of itsdriver transistor 285 and feedback bus 160 of the regulator. When itsdriver transistors 285 saturates during ionization delay the basecurrent in resistor 287 allows the base, and conseers provide to avoidthe unbalancing the regulator when ionization occurs'readily, as when acathode segment 60G is energized with several others in amultiplesegment'character or symbol. This ensures that the charging anddischarging of bias storage capacitor 175 remains approximately equal atthe designed ionization delay interval even though a special driver 2506is being operated with the others. Otherwise, capacitor 175 would beinadequately charged.

In the special driver for the minus symbol cathode of FIG. 5, damping isprovided in the circuit by capacitor 277 coupled between the drainelectrode of input transistor 260 and negative bias terminal 280. Thisdampens initial saturation of its driver transistor 285 and if itsfeedback to the regulator to allow ionization to occur in the display atthe lowest possible voltage. It also aids in preventing unbalancing ofthe bias circuit upon rapid ionization. Coupling. capacitor 289 iseliminated, or not, as desired. The special minus symbol cathode driver2506 of FIG. isotherwise similar to that illustrated in FIG. 4.

Also, a forward-biased diode 154 may be connected between the base ofregulator transistor 165 and a voltage divider formed of resistors 152and 182 connected between V,; terminal 150 and zener diode 185, forexample. This causes transistor 165 to follow variations in the V powersource and to keep capacitor 175 charged to a minimum level independentof whether the display has been recently operated. This limits transientpower demands of regulator transistor 165 when the display is firstoperated or operated after a long in.-

ac tivate period.

Although the preferred embodiments of the invention have been describedin detail, it should be understood that the present disclosure has beenmade by way of example only. Many modifications and variations of theinvention are possible in light of the above teachings. It is,therefore, to be understood that within the scope of the-appendedclaims, the invention maybe practiced otherwise than as specificallydisclosed.

What I claim is: '1. A system for operating a multiple position flatpanel display device which comprises a base plate and face plate spacedapart and hermeti-- cally sealed together along a perimeter to form anenvelope which is filled with an ionizable gas, a plurality ofconductive runs on said base plate, and a plurality of groups of cathodesegments on said base plate but insulated from said conductive runs,with each run being connected to one cathode segment in each group, eachsaid group of cathode segments comprising a character position, and ananode electrode for each of said groups of cathode segments,

said system comprising a power supply,

a separate anode driver coupled to each of the anode electrodes forapplying positive-going signals to the anode electrodes as eachcharacter position is energized, Y

a separate cathode driver having its output coupled to each of saidconductive runs for applying negative-going signals to selected onesofthe cathode electrodes concurrent with energization of the associatedanode electrode to display a character at each character position,

a source of input signals coupled to each cathode driver,

a first bus coupled between said power supply and through separateresistive paths to the output of each said cathode driver,

a second bus connected to the input of each said cathode driver, 7

a third bus coupled to a portion of each said cathode driver formaintaining bias potential thereon,

an active circuit element coupled between said second and third busesfor maintaining bias potential on said third bus,

a capacitor connected between said first and second buses for receivingcurrent from said active circuit element and storing charge, and thenapplying operating bias'potential to each of the cathode drivers, and

impedance means coupled between said capacitor and said activecircuitelement for charging the capacitor proportionally to the numberof cathode segments energized in each said group at each characterposition to regulate the potential across it so that the firingthreshold of the cathodes at the selected position in the device isexceeded and the cathodes exhibit cathode glow.

2. The system defined in claim 1 wherein said active circuit elementcomprises a first transistor having base, emitter, and collectorelectrodes with its emitter connected through a first resistiv e path tosaid capacitor and to said third bus, and its base electrode connectedthrough a second resistive path to said third bus, and its collectorelectrode connected to a source of bias potential, and

each said cathode driver comprises a second transistor having base,emitter, and collector electrodes, its base electrode being connected tothe base electrode of said first transistor, its emitter electrode beingconnected both through a capacitor to said source of input signals andthrough a diode to said third bus, and its collector electrode beingconnected to oneof said conductive runs and through one of saidresistive paths to said first bus.

3. A system for operating a multiple position flat panel display devicewhich comprises a base plate and face plate spacedapart and hermeticallysealed together along a perimeter to form an envelope which is filledwith an ionizable gas, a plurality of conductive runs on said baseplate, and a plurality of groups of cathode segments on said base platebut insulated from said conductive runs, with each run being connectedto one cathode seg ment in each group, each said group of cathodesegments comprising a character position, and an anode electrode foreach of said groups of cathode segments,

said system comprising a power supply,

a first bus extending from said power supply,

a second bus, a third bus, and a fourthbus,

a capacitor connected between said second and third buses,

a first transistor Connected between said third and fourth buses andhaving base, emitter, and collector electrodes,

said first transistor and its associated circuitry sensing the number ofcathodes energized and to be turned on at any one character position andpassing a charging current, proportional to said number of cathodes, tosaid capacitor, the charge developed therein being applied to saidsecond bus and to said cathode runs and to the associated cathodesegments, and

a cathode driver circuit for each of said conductive runs and for eachsaid one cathode, segment in each said group of cathode segments,

, each said driver circuit including a source of input signals, and asecond transistor having base, emitter, and collector electrodes, theemitter electrode being coupled both to said source of input signals andto'said third bus, the base electrode being connected to said fourthbus,and the collector electrode being connectedboth to said second bus andto one of said conductive runs, whereby when a source of input signalsis operated and applies a signal to the second transistor in theassociated cathode drive circuit, said second electrode of said firsttransistor, and a second resistor coupled between said third bus and oneside of said capacitor and the emitter electrode of said firsttransistor, said first resistor sensing current flow in the cathodesegments energized by said signal sources.

5. The system defined in claim 3 wherein, in each cathode drivercircuit, the emitter of the second transistor is connected both througha diode to said third bus and through a capacitor to its source of inputsignals.

6. The system defined in claim 3 wherein, in each cathode drivercircuit, the collector of the second transistor is connected through aresistor and diode to said second bus.

1. A system for operating a mulTiple position flat panel display devicewhich comprises a base plate and face plate spaced apart andhermetically sealed together along a perimeter to form an envelope whichis filled with an ionizable gas, a plurality of conductive runs on saidbase plate, and a plurality of groups of cathode segments on said baseplate but insulated from said conductive runs, with each run beingconnected to one cathode segment in each group, each said group ofcathode segments comprising a character position, and an anode electrodefor each of said groups of cathode segments, said system comprising apower supply, a separate anode driver coupled to each of the anodeelectrodes for applying positive-going signals to the anode electrodesas each character position is energized, a separate cathode driverhaving its output coupled to each of said conductive runs for applyingnegative-going signals to selected ones of the cathode electrodesconcurrent with energization of the associated anode electrode todisplay a character at each character position, a source of inputsignals coupled to each cathode driver, a first bus coupled between saidpower supply and through separate resistive paths to the output of eachsaid cathode driver, a second bus connected to the input of each saidcathode driver, a third bus coupled to a portion of each said cathodedriver for maintaining bias potential thereon, an active circuit elementcoupled between said second and third buses for maintaining biaspotential on said third bus, a capacitor connected between said firstand second buses for receiving current from said active circuit elementand storing charge, and then applying operating bias potential to eachof the cathode drivers, and impedance means coupled between saidcapacitor and said active circuit element for charging the capacitorproportionally to the number of cathode segments energized in each saidgroup at each character position to regulate the potential across it sothat the firing threshold of the cathodes at the selected position inthe device is exceeded and the cathodes exhibit cathode glow.
 2. Thesystem defined in claim 1 wherein said active circuit element comprisesa first transistor having base, emitter, and collector electrodes withits emitter connected through a first resistive path to said capacitorand to said third bus, and its base electrode connected through a secondresistive path to said third bus, and its collector electrode connectedto a source of bias potential, and each said cathode driver comprises asecond transistor having base, emitter, and collector electrodes, itsbase electrode being connected to the base electrode of said firsttransistor, its emitter electrode being connected both through acapacitor to said source of input signals and through a diode to saidthird bus, and its collector electrode being connected to one of saidconductive runs and through one of said resistive paths to said firstbus.
 3. A system for operating a multiple position flat panel displaydevice which comprises a base plate and face plate spaced apart andhermetically sealed together along a perimeter to form an envelope whichis filled with an ionizable gas, a plurality of conductive runs on saidbase plate, and a plurality of groups of cathode segments on said baseplate but insulated from said conductive runs, with each run beingconnected to one cathode segment in each group, each said group ofcathode segments comprising a character position, and an anode electrodefor each of said groups of cathode segments, said system comprising apower supply, a first bus extending from said power supply, a secondbus, a third bus, and a fourth bus, a capacitor connected between saidsecond and third buses, a first transistor connected between said thirdand fourth buses and having base, emitter, and collector electrodes,said first transistor and its associated circuitry sensing thE number ofcathodes energized and to be turned on at any one character position andpassing a charging current, proportional to said number of cathodes, tosaid capacitor, the charge developed therein being applied to saidsecond bus and to said cathode runs and to the associated cathodesegments, and a cathode driver circuit for each of said conductive runsand for each said one cathode segment in each said group of cathodesegments, each said driver circuit including a source of input signals,and a second transistor having base, emitter, and collector electrodes,the emitter electrode being coupled both to said source of input signalsand to said third bus, the base electrode being connected to said fourthbus, and the collector electrode being connected both to said second busand to one of said conductive runs, whereby when a source of inputsignals is operated and applies a signal to the second transistor in theassociated cathode drive circuit, said second transistor is driven tosaturation before the associated cathode turns on and current flowsthrough said first transistor to charge said capacitor proportionally tothe number of cathodes to be turned on, said charge being applied as agenerally negative potential to said second bus and to the associatedcathodes to be turned on.
 4. The system defined in claim 3 and includinga first resistor coupled between said third bus and the base electrodeof said first transistor, and a second resistor coupled between saidthird bus and one side of said capacitor and the emitter electrode ofsaid first transistor, said first resistor sensing current flow in thecathode segments energized by said signal sources.
 5. The system definedin claim 3 wherein, in each cathode driver circuit, the emitter of thesecond transistor is connected both through a diode to said third busand through a capacitor to its source of input signals.
 6. The systemdefined in claim 3 wherein, in each cathode driver circuit, thecollector of the second transistor is connected through a resistor anddiode to said second bus.